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Morgan 2023-11-19 12:04:39 +09:00
parent 81e51f0e7f
commit 0cdb352220
2 changed files with 26 additions and 27 deletions
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44
content/posts/2022-11-19-Linux-Kernel-sys_fork.md → content/posts/2023-11-11-Linux-Kernel-sys_fork.md
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@ -1,11 +1,11 @@
--- ---
title: Linux Kernel, syscalls title: Linux Kernel, syscalls
date: 2022-11-19T date: 2023-11-11T01:22:30Z
slug: linux-kernel-sys-fork slug: linux-kernel-sys-fork
description: "" description: ""
--- ---
#### sys_fork() ### sys_fork()
```asm ```asm
.align 2 .align 2
@ -23,7 +23,7 @@ _sys_fork:
1: ret 1: ret
``` ```
##### `FUNCTION find_empty_process()` #### `FUNCTION find_empty_process()`
```assembly ```assembly
A: A:
@ -49,11 +49,12 @@ A:
##### `FUNCTION copy_process` #### `FUNCTION copy_process`
`<- nr, EBP, EDI, ESI, GS, EBX~EDX, CS~FS, EIP, EFLAGS, ESP, SS`
`-> INT`
```
<- nr, EBP, EDI, ESI, GS, EBX~EDX, CS~FS, EIP, EFLAGS, ESP, SS
-> INT
```
```assembly ```assembly
TASK_STRUCT P TASK_STRUCT P
@ -117,24 +118,15 @@ RET last_pid
"nr" passed is the index of the new task in the task array, where each element corresponds to a process slot. - "nr" passed is the index of the new task in the task array, where each element corresponds to a process slot.
- fork() copies the parent's kernel context, as well as general registers and segment selectors required for a new process to run in user space.
fork() copies the parent's kernel context, as well as general registers and segment selectors required for a new process to run in user space. - It creates a new task structure from a new free page and sets up default values and certain parameters inherited from the parent, such as process ID, priority, and execution times.
- Then it copies memory regions from the parent to the new process, referred to by "nr," which is the index of the new process in the task array.
It creates a new task structure from a new free page and sets up default values and certain parameters inherited from the parent, such as process ID, priority, and execution times. - Changes the parent process's working directory (PWD) and root directory reference counters, incrementing them by 1 to reflect the new child process now also using these resources.
- Sets the Task State Segment (TSS) and Local Descriptor Table (LDT) entries, which are x86-specific structures used for task switching and memory segmentation, respectively.
Then it copies memory regions from the parent to the new process, referred to by "nr," which is the index of the new process in the task array. - TSS holds information about the task's stack for privilege level changes and also the hardware context when a task switch occurs.
- LDT is a segment descriptor table that stores descriptors for local segments, giving a task its own set of segment registers.
Changes the parent process's working directory (PWD) and root directory reference counters, incrementing them by 1 to reflect the new child process now also using these resources. - Finally, it assigns the newly created task structure, p, to the task array at index "nr." This effectively makes the new task available for scheduling.
Sets the Task State Segment (TSS) and Local Descriptor Table (LDT) entries, which are x86-specific structures used for task switching and memory segmentation, respectively.
TSS holds information about the task's stack for privilege level changes and also the hardware context when a task switch occurs.
LDT is a segment descriptor table that stores descriptors for local segments, giving a task its own set of segment registers.
Finally, it assigns the newly created task structure, p, to the task array at index "nr." This effectively makes the new task available for scheduling.
### `_sys_fork()`
"sys_fork" finds an empty process ID using the search loop in `_find_empty_process`, then it invokes `_copy_process` to clone the parent's kernel context to the new process. This sets up a complete environment for the new process to run independently from the parent, but initially as a nearly identical copy. "sys_fork" finds an empty process ID using the search loop in `_find_empty_process`, then it invokes `_copy_process` to clone the parent's kernel context to the new process. This sets up a complete environment for the new process to run independently from the parent, but initially as a nearly identical copy.

9
scripts/remote.sh
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@ -1 +1,8 @@
ssh web /srv/blog/scripts/update.sh HOST=$1
if [[ -z $1 ]];
then
HOST="web"
echo $HOST
fi
ssh $HOST /srv/blog/scripts/update.sh